High Nitrogen Steels

High-nitrogen steels (HNS) have attracted raised attention due to their exceptional mechanical properties, corrosion resistance and wear resistance. These properties have led to increased applications in energy production, transportation, pulp and paper, oil and gas, chemical industries and so forth. To foster scientific and technical exchanges between experts from the steel industry, research organizations and end-users concerning this specific steel category, the International Conference on High Nitrogen Steels was initiated in Lille (France) in 1988, continued in Aachen (Germany) in 1990, Kiev (Ukraine) in 1993, Kyoto (Japan) in 1995, Helsinki/Stockholm (Finland/Sweden) in 1998, Chennai (India) in 2002, Schaffhausen (Switzerland) in 2003, Ostend (Belgium) in 2004, Jiuzhaigou Valley (China) in 2006, Moscow (Russia) in 2009, Chennai (India) in 2012, and Hamburg (Germany) in 2014. The 13th International Conference on High Nitrogen Steels (HNS2021) was held in a hybrid format on 14th Sep. 2021 in Shanghai due to COVID-19-related travel restrictions. The conference was chaired by Prof. Han Dong (Shanghai University, China) and Prof. Guocai Chai (Sandvik Materials Technology AB/Linköping University, Sweden). The conference program comprised 8 plenary speeches and 23 oral presentations delivered by experts from research institutes, universities, and companies from over 11 countries. Prof. Han Dong opened the conference with a speech on “Look at high nitrogen austenitic stainless steels at present”. The conference featured four parallel sections covering topics: nitrogen alloying mechanisms, mechanical properties, processing and production of HNS, and their applications and in-service properties. The conference attracted over 400 online participants. This special section of Steel Research International publishes 7 highlighted works presented at HNS2021, following the journal's regular review process. Prof. Guocai Chai presents “Roles of Nitrogen on TWIP in Advanced Austenitic Stainless Steels”. The article discusses the effect of nitrogen on deformation mechanisms at cryogenic temperature and the resulting mechanical and magnetic properties. (see front cover and article 2200359). Prof. Toshihiro Tsuchiyama reports on “Nitrogen-Enhanced Temperature Dependence of Grain Refinement Strengthening in Austenitic Stainless Steel”. The work reveals that nitrogen significantly enhances the increment of the Hall-Petch coefficient at low temperatures in high-N-containing 316L steel. As explained by the pileup model, nitrogen contributes substantially to raising the critical grain boundary shear stress and enhancing the grain boundary bonding force at low temperatures. (See back cover and article 2200428). Prof. Zhouhua Jiang and Prof. In-Ho Jung report on “Thermodynamics of Nitrogen in Molten Fe–Cr–Mn–C–N Alloys” by using the Modified Quasichemical Model with the consideration of short-range ordering. They determined a set of new self-consistent binary and ternary model parameters for the Fe-Cr-Mn-C-N solution and applied them to predict the N solubility in this multi-component molten alloys, which is vital for the process optimization of high N stainless steels, ferritic stainless steels, TWIP steels, etc. (see article 2200510). Prof. Hua-Bing Li presents “A Promising Pressurized Duplex Manufacturing Route of High Nitrogen Stainless Steel“ by incorporating the pressurized induction melting (PIM) process to fulfil nitrogen alloying, deoxidation and desulfurization and pressurized electro slag remelting (PESR) process to further desulfurize, remove large-size inclusions and elevate solidification quality. High nitrogen stainless bearing steel 30Cr15Mo1N (DIN 1.4108) has been successfully manufactured and demonstrated improved mechanical and corrosion properties compared to the single-stage PIM process (see article 2200321). Prof. Mei Zhang reports “Hot Deformation Behavior and 3D Processing Maps of Mn18Cr18N Steel”, which established a 3D processing map of Mn18Cr18N steel based on controlled hot deformation parameters using a Gleeble-3500 thermomechanical simulator and dynamic materials model. The optimum hot working temperature and strain rate domains 1000-1150°C/0.002-0.1 s−1 with effective dynamic recrystallization have been proposed (see article 2200358). Prof. Wei Peng presents “Insights into the Impact Behavior and Deformation Substructure Evolution of the N-Bearing QN1803 and 304 Stainless Steels”. The 0.26%N bearing QN1803 austenitic steel demonstrated a pronounced ductile-brittle transition temperature, which has higher impact energy than 304 at a high-temperature domain of 0-100°C. Its postponed fracture occurrence was attributed to the promoted fault growth in N-enriched zones. At low temperatures, the QN1803 has low stacking fault energy and reveals high local shear at the stacking faults, leading to local fracture initiation (see article 2200508). Prof. Ke Yang reviews high-nitrogen nickel-free stainless steel as an attractive biomedical metallic material with high strength, high fatigue resistance, high pitting corrosion resistance and excellent biocompatibility. It calls for further studies concerning the influence of transformation products from nitrogen on biological functions during service. The Ni-free high nitrogen austenitic stainless steels may have expanding applications as biocompatible metallic materials (see article 2200355). This special Issue section covers several important aspects of this specific steel group, which serve as milestones of the relevant research activities. The excellent strength-toughness properties combined with exclusive physical and functional properties may drive growing research interests in HNS. The in-depth understanding of its physical metallurgy, deformation mechanisms, as well as innovative production process opens the door for further knowledge exchange among researchers in this field. Let's look forward to the next international meeting on this interesting topic. The authors declare no conflict of interest. Han Dong is a professor at School of Materials Science and Engineering, Shanghai University, China. He is Chair of the 13th International Conference on High Nitrogen Steels, HNS 2021. He has long academic and industrial experience as metallurgical and materials science researcher in China. He is currently the dean of School of Materials Science and Engineering, Shanghai University, as well as the director of Zhejiang Institute of Advanced Materials, Shanghai University. He has coauthored over 300 publications and patents as well as received many awards including the first prize of national science and technology progress award. His research interests include phase transformation, alloy design, and deformation mechanisms of advanced high-strength structural steels and special steels. Guocai Chai is adjunct professor in engineering materials, Linköping University, Sweden and the global group expert at Alleima AB (Sandvik group earlier), Sweden. He is co-Chair of the 13th International conference on High Nitrogen Steels, HNS 2021. He is the board member of the Swedish Royal Mechanics Society and the board member of Swedish Society for Materials and Technology. He is the management committee member of the European creep collaboration committee, ECCC. He was an EU expert for Horizon 2020/RFCS program and the international independent expert for seven countries. His research areas are material design and development, microstructure, and properties. Xiaofei Guo is professor at School of Materials Science and Engineering, Shanghai University, China. She is the conference Secretary of the 13th International Conference on High Nitrogen Steels, HNS 2021. She received her Ph.D. in Steel Institute, RWTH Aachen University, Germany, in 2012 and worked as a senior researcher there afterwards. She obtained professorship from School of Materials Science and Engineering, Shanghai University, in 2021. She focuses on the alloy and microstructural design of advanced high-strength steels with concerns of their in-service properties, especially hydrogen embrittlement resistance.